Four MPs of Greece's neo-Nazi party Golden Dawn have appeared before an Athens court accused of participating in a criminal organisation.

Ilias Panagiotaros, Ilias Kasidiaris, Yannis Lagos and Nikos Michos were taken to court by anti-terrorist squad officers, as a few dozen Golden Dawn supporters who had gathered outside applauded.

The four were arrested as part of a crackdown on the far-right group that followed the killing of anti-facist rapper Pavlos Fyssas.

Fyssas, nicknamed Killah P, was stabbed to death outside a café in the Keratsini area west of Athens.

Police arrested a 45-year-old supporter of Golden Dawn, George Roupakias, over the killing and raided the party headquarters in the Greek capital.

Another 21 people linked to the extremist movement were subsequently held by authorities and arrest warrants issued for 10 more.

Party leader Nikolaos Michaloliakos and his deputy Christos Pappas were among the arrested, and are expected to appear in court later this week.

Prosecutors allege that the attack against Fyssas was premeditated and the party leadership knew about the murder, as Golden Dawn operates according to a strict hierarchical command structure.

Golden Dawn has denied any connection to the killing.

The far-right party has made substantial gains from Greece's deep economic crisis, blaming the country's large immigrant population as one of the causes.

It won 18 seats in the Greek parliament, gaining almost 7% of preferences in the two elections last year, and its members have been accused of perpetrating a spate of violent attacks against migrants.

The party rejects the neo-Nazi label, denying it draws inspiration from Hitler's movement.

The Nazi occupation of Greece during the Second World War is still a sensitive issue to many Greek nationalists who feed the party's ranks. However its members are often depicted mimicking the Nazi salute and the Nazi anthem has been played at party events.

Police searches related to Fyssas's death revealed how party officials' filled their homes with posters of Adolf Hitler, and assorted Nazi memorabilia. Illegal firearms were also retrieved.

Photos of Pappas's house showed the party's parliamentary spokesman had put up a personal collection of Nazi and Fascism items, including a Waffen SS poster and helmet, an Adolf Hitler street sign, a toy Nazi soldier, swastikas and wine bottles labelled with photos of Italian fascist leader Benito Mussolini.